7D not always 8fps

There's a note on page 93 of the manual "In low-light areas or indoors, the continuous shooting speed may become slower even if a faster shutter speed is set."

Regardless of mode & shutter speed, in low light, the burst speed does appear to slow down to 3-4 fps. Even with manual focus & Manual mode with a high shutter speed set. This can be overridden in Av & Tv by using AE Lock, but there is no workaround when shooting in M. Canon says it's their new metering system slowing the framerate down (accuracy over quantity), but why should this apply in M? The camera is not calculating exposure.

To demonstrate the phenomenon, and to prove it isn't shutter speed, buffer or focus related, set the lens to manual focus, mode to M, shutter speed to 1/1000, aperture to whatever, high-speed drive mode, low quality JPG. Point the camera directly at a light source and hold down the shutter. Should fire around 8fps. Still holding the shutter release, point the lens at the ground, or cover it with your hand. The burst will slow down. Uncover, rate goes back up.

Normally this would not be a problem in decent lighting (level of light where the fps slows down is also dependent on the speed of the lens), but I can see it being an issue shooting strobed action in a studio, for example, or any other burst you want to shoot indoors.

Live view with silent mode enabled does not exhibit this slow down "feature", but if I recall, strobes will not fire with silent mode enabled.